Cp[TmMe]ZrCl2, a tris(2-mercapto-1-methylimidazolyl)hydroborato complex of zirconium and a new type of precatalyst for olefin polymerization

Cp[Tm-Me]ZrCl2, the first tris(2-mercapto-1-methylimidazolyl) hydroborato complex of zirconium, is obtained by reaction of CpZrCl3 with [Tm-Me] K. The molecular structure of Cp[Tm-Me]ZrCl2 has been determined by X-ray diffraction, and the geometry closely resembles the bent-metallocene motif of Cp2ZrCl2. An important distinction, however, is that Cp[Tm-Me]ZrCl2 is chiral, with C-1 symmetry. The chirality of Cp[Tm-Me]ZrCl2 is a consequence of the fact that the [Tm-Me] ligand exhibits a propeller-like twist such that it has local C-3 symmetry and is therefore devoid of a mirror plane. Variable-temperature H-1 NMR studies demonstrate that enantiomer interconversion does not occur on the NMR time scale. In combination with methylalumoxane, Cp[Tm-Me]ZrCl2 produces an active catalyst for ethylene polymerization.